Silicon Motion SM2256 SSD Controller Preview: TLC for Everyone

Final Words

To get the elephant in the room out first, I'm not overly satisfied with the performance. The SM2256 is slower than the other TLC SSDs (850 EVO & Ultra II) on the market and not just by an insignificant margin. Especially small size random IOs are rather slow, which impact the overall performance because many IOs in client workloads are 4KB and random in nature. For very light IO workloads that obviously won't be a major issue, but anything more IO intensive (like virtualization) could be severely impacted by SM2256's high latency. To be frank, I never expected the SM2256 to perform like the SM2246EN because no controller can get around the performance limitations of TLC NAND, but given how well the SM2246EN performs I was expecting the SM2256 to be faster than it is.

Aside from performance, the other problem with SM2256 is its power consumption. The part I absolutely love in the SM2246EN is its extremely low power consumption, but the SM2256 practically doubles the power draw that makes it one of the least efficient drives we have tested. Again, expecting the SM2256 to be as efficient as the SM2246EN wouldn't be fair because TLC inherently has higher power consumption as it needs a higher number of program-verify iterations, but even then doubled power consumption is a bit more than I was looking forward to. 

I do wonder how big of a difference the NAND makes, though. As I mentioned on page one, we will likely never see this configuration on the retail market because Samsung doesn't sell its TLC to third parties in large quantities, so I'm not sure if Silicon Motion has spent a ton of resources in optimizing the firmware for NAND that won't be used outside of engineering samples. I certainly hope that the SM2256 performs better with NAND from other vendors because as it stands the performance is quite underwhelming against the competition, but nothing that couldn't be fixed with better optimization. After all, the sample I have doesn't have the final retail firmware in it, so we will have to wait for shipping drives before drawing the final verdict on the SM2256.

In any case, it will all boil down to pricing anyway. If Silicon Motion's OEM partners can drive the prices down with the SM2256, I will be totally fine with the performance because the SM2256 is still more than fine for basic usage. TLC SSD pricing was actually one of the things I was very vocal about at Computex because OEMs can't price their TLC drives similarly to the MLC ones and expect it to be a good sale. TLC isn't as good as MLC and that's a fact that nobody can deny. Especially after Samsung's issues with TLC the market has become more skeptical about TLC in general, so saving a few bucks isn't enough anymore for the educated buyers to choose TLC over MLC -- I think the difference has to be in the order of 10% or so to be worth the lower performance and possible long-term reliability risks that TLC brings. I do believe that the SM2256 is a vehicle capable of delivering such cost savings, but for now we will just need to wait and see what happens.